In this installment of the Zero Woman series, Rei, the number-one assassin of the Tokyo Police Department's secret Zero Division, has been assigned to take out a notorious gangster responsible for dozens of murders. At the same time, she must protect the gangster's mistress from the hitmen who want to keep her from telling the police what she knows. At first, both women are upset about the arrangement, but they eventually come to appreciate each other.

Mari is a high school teacher who is earnest and somewhat cold. Tired of her monotonous days, she discovered a secret game: wandering around Roppongi at night and seducing men. She enjoys the pleasure of lewd acts with strangers and finds temporary peace. Her student Toshihiko, who happens to witness her nighttime appearance, is captivated by Mari's seductive figure before he knows it...